Chemical-mechanical polishing (CMP) is the process of removing material from a work piece to create a smooth planar surface. In a conventional CMP assembly, the work piece is secured in a carrier head such that the surface to be polished is exposed. The exposed surface of the wafer is then held against a polishing pad. One side of the polishing pad has a polishing surface thereon, and an opposite side is mounted to a rigid platen. Pressure is exerted on a back surface of the work piece by a flexible diaphragm in the carrier head in order to press the work piece front surface against the polishing pad. Polishing slurry is introduced to the polishing surface while the work piece and/or polishing pad are moved in relation to each other by means of motors connected to the shaft and/or platen. This relative motion may be linear, rotational, orbital or other such multi-directional motion. One way that the slurry is supplied to the polishing surface is through one or more holes in the polishing pad. The holes in the polishing pad are in communication with a supply source via holes or passageways provided in the platen. Another way that the slurry is supplied to the polishing surface is by metering the slurry onto the polishing pad from a nozzle.
The combination of chemical reactions and mechanical forces of the CMP process results in removal of material from the work piece front surface to form a substantially planar surface. One requisite for removing material from the work piece surface at a high rate (“removal rate”) and with a uniform removal rate across the entire surface is the rotation of the polishing pad and/or the work piece in a manner whereby any grooves or other topographical features on the polishing pad traverse the wafer surface in a uniform manner. A non-uniform material removal rate will result if particular grooves or other topographical features on the polishing pad are biased to repeatedly traverse particular wafer surface regions during polishing.
The pattern traced on the wafer surface by a given point on the polishing pad is determined by the kinematics of the particular CMP apparatus being employed and on the particular settings for the process parameters controlling operation of that apparatus. For example, if the CMP apparatus is an orbital CMP apparatus, the wafer undergoes a number of motions relative to the polishing pad: orbital motion, rotational motion, and angular oscillation motion. The kinematics of the CMP operation depend on the parameters governing these motions such as orbiting radius, orbiting speed, wafer rotation speed, angular oscillation range, oscillation speed, and upper-to-lower head offset (the offset of the axis of the carrier head with respect to the center of the polishing pad). The combination of these parameters affects the “kinematical pattern” on the wafer traced by a particular point on the polishing pad, and, indirectly, the probability of a specific location on the wafer being exposed to a groove or other topographical feature on the polishing pad. These parameters and their effect will vary depending on the particular type of CMP apparatus being employed.
As an alternative to traditional CMP, electrochemical mechanical polishing (ECMP) can be used for polishing the work piece. ECMP is a type of CMP process that involves removal of material from the surface of the work piece through the action of an electrolyte solution, electricity, and relative motion between the work piece and the polishing pad. The ECMP process has the same requirement for uniform removal of material from the wafer and the need for a uniform “kinematical pattern” traced by relative motion between the wafer and the polishing pad.
Accordingly, it is desirable to provide a chemical mechanical polishing assembly that achieves a controllable and uniform material removal rate during a CMP process. In addition, it is desirable to provide a CMP apparatus that creates a uniform kinematical pattern on the wafer surface. This may be accomplished by utilizing a polishing pad that includes topographical features that uniformly traverse a wafer surface during a CMP process. It may also be accomplished by optimizing the process parameters that control the kinematics of the CMP process during operation of the apparatus. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.